Ecological studies on the deep-water pelagic community of Korsfjorden, western Norway

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Abstract
Data are presented for Thysanoessa inermis, T. longicaudata, T. raschii, Nematoscelis megalops, Thysanopoda acutifrons, and Nyctiphanes couchii obtained from horizontal samples taken on a monthly basis at six depths. Thysanoessa spp. and N. megalops have a one-year life cycle and no individuals have been recognized which have completed a second year. Spawning seems to occur in spring/ early summer, probably slightly later in T. raschii than in the other three species. T. acutifrons is considered to have a two-year life cycle, in deeper water, with the possibility of spawning again at three years of age; the spawning season is in early summer, a little later than the other species. N. couchii is an irregular visitor. Successive generations, particularly of T. inermis where recruitment and mortality are described mathematically, can show marked differences in abundance. Growth of all species, and of Meganyctiphanes norvegica, is expressed in a single expression, the only variable being the asymptotic length. The values of the constants for T. acutifrons are rather different.